Transceiver module with PCB having embedded traces for EMI control

ABSTRACT

A PCB is provided that is suitable for use in applications where EMI control is of interest. The PCB includes circuitry that communicates with an edge connector having edge traces located on its surface. Additionally, embedded traces are disposed within the dielectric material of the PCB, and each embedded trace electrically connects an edge trace with a corresponding median trace located on a surface of the PCB. An embedded ground layer substantially disposed within the dielectric material defines an area within the dielectric material through which the embedded traces pass. Finally, one or more vias are provided that extend through the dielectric material of the PCB and are filled with a conductive material. The vias are electrically connected to the embedded ground layer and configured to electrically communicate with an associated module. In this way, a structure is implemented that facilitates control of electromagnetic radiation emitted by the PCB circuitry.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a division, and claims the benefit, of U.S.patent application Ser. No. 10/425,090, entitled ELECTROMAGNETICINTERFERENCE CONTAINMENT TRANSCEIVER MODULE, filed Apr. 28, 2003, which,in turn, claims the benefit of U.S. Provisional Patent Application No.60/419,444, filed Oct. 17, 2002. Both of the aforementioned applicationsare incorporated herein in their respective entireties by thisreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention generally relates to optical modules. Moreparticularly, exemplary embodiments of the invention concern an opticalmodule that includes

[0004] 2. Related Technology

[0005] Fiber optics are increasingly used for transmitting voice anddata signals. As a transmission medium, light provides a number ofadvantages over traditional electrical communication techniques. Forexample, light signals allow for extremely high transmission rates andvery high bandwidth capabilities. Also, light signals are resistant toelectromagnetic interferences that would otherwise interfere withelectrical signals. Light also provides a more secure signal because itdoesn't allow portions of the signal to escape from the fiber opticcable as can occur with electrical signals in wire-based systems. Lightalso can be conducted over greater distances without the signal losstypically associated with electrical signals on copper wire.

[0006] While optical communications provide a number of advantages, theuse of light as a transmission medium presents a number ofimplementation challenges. In particular, the data carried by a lightsignal must be converted to an electrical format when received by adevice, such as a network switch. Conversely, when data is transmittedto the optical network, it must be converted from an electronic signalto a light signal. A number of protocols define the conversion ofelectrical signals to optical signals and transmission of those optical,including the ANSI Fibre Channel (FC) protocol. The FC protocol istypically implemented using a transceiver module at both ends of a fiberoptic cable. Each transceiver module typically contains a lasertransmitter circuit capable of converting electrical signals to opticalsignals, and an optical receiver capable of converting received opticalsignals back into electrical signals.

[0007] Typically, a transceiver module is electrically interfaced with ahost device—such as a host computer, switching hub, network router,switch box, computer I/O and the like—via a compatible connection port.Moreover, in some applications it is desirable to miniaturize thephysical size of the transceiver module to increase the port density,and therefore accommodate a higher number of network connections withina given physical space. In addition, in many applications, it isdesirable for the module to be hot-pluggable, which permits the moduleto be inserted and removed from the host system without removingelectrical power. To accomplish many of these objectives, internationaland industry standards have been adopted that define the physical sizeand shape of optical transceiver modules to insure compatibility betweendifferent manufacturers. For example, in 2000, a group of opticalmanufacturers developed a set of standards for optical transceivermodules called the Small Form-factor Pluggable (“SFP”) TransceiverMulti-Source Agreement (“MSA”), incorporated herein by reference. Inaddition to the details of the electrical interface, this standarddefines the physical size and shape for the SFP transceiver modules, andthe corresponding host port, so as to insure interoperability betweendifferent manufacturers' products. There have been several subsequentstandards, and proposals for new standards, including the XFP MSA for 10Gigabit per second modules using a serial electrical interface, thatalso define the form factors and connection standards for pluggableoptoelectronic modules, such as the published draft version 0.92 (XFPMSA), incorporated herein by reference.

[0008] As optical transmission speed provided by electronic modulesincreases, additional problems arise. For example, electronic devicesand components operating at high frequencies typically emit signalsreferred to as electromagnetic interference. This electromagneticinterference, referred to as “EMI”, is electrical noise in the form ofan electromagnetic wave. The phenomenon is undesirable because EMI caninterfere with the proper operation of other electrical components.Optical transceiver packages, especially those operating at hightransmission speeds, are especially susceptible to emitting EMI. Inparticular, the physical configuration of existing transceiver modulesdoes a poor job of containing EMI—especially as the generating speed ofthe module increases. For example, as is shown in FIGS. 7A through 8C, atransceiver module 8 typically includes a housing 5 that contains aprinted circuit board 10 and associated electrical and opticalcomponents. However, the housing 5 does not completely enclose theprinted circuit board 10. Instead, a portion of the printed circuitboard 10 is formed as an edge connector 12. The edge connector 12includes a number of high speed traces for communicating signals to andfrom the electrical contacts on the edge connector 12. In operation, theedge connector 12 is capable of electrically and physically interfacingwith a corresponding host connector 702 that is positioned on a hostboard 700.

[0009] Thus, in order for the edge connector 12 to be exposed externallyto the module, the module housing 5 must provide an opening, shown at 20in FIG. 6B. Moreover, insofar as the housing 5 is typically constructedof a conductive material, the opening 20 typically provides a minimumclearance area (the diagonal dimension of which is represented as “X” inFIG. 6B), so as to not electrically interfere with the high speed traceson the edge connector portion of the board 10. Unfortunately, thisopening 20 also allows for the emission of an unacceptable amount ifEMI; the emission is especially problematic as transmission speedsincrease.

[0010] Therefore, there is a need in the industry for a pluggablemodule, such as an optoelectronic transceiver module, that is configuredso as to minimize the emission of EMI. Preferably, the moduleconfiguration could be used in environments having high frequency datasignal transmissions. Moreover, the module configuration should notaffect the data signal integrity or the speed capabilities of themodule. In addition, the electronic module should be implemented in amanner that meets existing standard form factors. Preferably, the moduleshould maintain the ability to properly dissipate heat from thecomponents inside the module.

BRIEF SUMMARY OF AN EXEMPLARY EMBODIMENT OF THE INVENTION

[0011] Briefly summarized, exemplary embodiments of the presentinvention are directed to a PCB suitable for use in connection withelectronic modules, such as optical transceiver modules for example. Anexemplary PCB includes a variety of electronic components disposed onits surface, as well as a connector portion formed at one end. Theconnector portion includes a plurality of conductive edge traces thatinterconnect with traces of a host system, such as a computer, signalrouter, or other input/output device, when an electronic module whereinthe PCB is disposed is interfaced with the host system.

[0012] The PCB also includes embedded traces disposed within thedielectric material of the PCB and electrically connecting an edge tracewith a corresponding median trace located on a surface of the PCB. Anembedded ground layer substantially disposed within the dielectricmaterial defines an area within the dielectric material through whichthe embedded traces pass. Finally, one or more vias are provided thatextend through the dielectric material of the PCB and are filled with aconductive material. The vias are electrically connected to the embeddedground layer and configured to electrically communicate with anassociated electronic module.

[0013] In this way, a structure is implemented that facilitates controlof electromagnetic radiation emitted by the PCB circuitry. These, andother, aspects of the present invention will become more fully apparentfrom the following description and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order that the manner in which the above recited and otheradvantages and features of the invention are obtained, a more particulardescription of the invention briefly described above will be given bymaking reference to a specific embodiment that is illustrated in theappended drawings. These drawings depict only a few embodiments of theinvention and are not to be considered limiting of its scope:

[0015]FIG. 1A is an exploded perspective view of a transceiver moduleconfigured to contain EMI waves in accordance with one embodiment of thepresent invention;

[0016]FIG. 1B is an exploded perspective view of the rear end of atransceiver module configured to contain EMI waves in accordance withone embodiment of the present invention;

[0017]FIG. 1C is an exploded perspective view of the bottom side of atransceiver module configured to contain EMI waves in accordance withone embodiment of the present invention;

[0018]FIG. 1D is an exploded perspective view of the bottom side of therear end of a transceiver module configured to contain EMI waves inaccordance with one embodiment of the present invention;

[0019]FIG. 2A is another perspective view of a transceiver moduleconfigured to contain EMI waves in accordance with one embodiment of thepresent invention;

[0020]FIG. 2B is a rear view of the transceiver module of FIG. 2A;

[0021]FIG. 2C is a side view of the transceiver module of FIG. 2A;

[0022]FIG. 2D illustrates a cutaway rear view taken along lines 2D-2D ofFIG. 2C;

[0023]FIG. 2E illustrates a close up cutaway rear view taken along lines2E in FIG. 2D;

[0024]FIG. 3A illustrates an exploded view of another embodiment of atransceiver module;

[0025]FIG. 3B is an exploded view showing additional details of the rearend of the transceiver module of FIG. 3A;

[0026]FIG. 3C is an exploded perspective view of the bottom of thetransceiver module of FIG. 3A;

[0027]FIG. 3D is an exploded view of the rear end of the transceivermodule of FIG. 3A;

[0028]FIG. 4A is another perspective view of the transceiver module ofFIG. 3A;

[0029]FIG. 4B is a rear view of the transceiver module of FIG. 4A;

[0030]FIG. 4C is a side view of the transceiver module of FIG. 4A;

[0031]FIG. 4D is a cutaway rear view of the transceiver module takenalong lines 4D-4D in FIG. 4C;

[0032]FIG. 4E is a close up cutaway view of the transceiver module takenalong lines 4E in FIG. 4D;

[0033]FIG. 5A is an end view of a transceiver module configured inaccordance with another embodiment of the present invention;

[0034]FIG. 5B is a close-up cut away view of the transceiver moduletaken along lines 5B in FIG. 5A;

[0035]FIG. 6A illustrates a perspective view of a printed circuit boardportion in accordance with yet another alternative embodiment of thepresent invention;

[0036]FIG. 6B illustrates a cutaway rear view of a printed circuit boardtaken along lines 6B in FIG. 6A; and

[0037]FIGS. 7A-8C show various exemplary views of prior art modules.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0038] Reference will now be made to the drawings to describe exemplaryembodiments of the invention. It is to be understood that the drawingsare diagrammatic and schematic representations of such exemplaryembodiments, and are not limiting of the present invention, nor are theynecessarily drawn to scale.

[0039] In general, the present invention relates to an electronicpluggable module that is structured in a manner that minimizes theemission of potentially harmful EMI waves. In preferred embodiments, themodule maintains a low profile, and conforms with the physicaldimensions set forth by existing industry standards. In addition, EMIshielding is provided in a manner that does not interfere with theelectronic performance of the module. Likewise, the module isconstructed so as to dissipate heat efficiently and thereby avoidoverheating of the electrical or optical components. Although thepreferred embodiments are described in the context of an optoelectronictransceiver module, it will be appreciated that teachings of the presentinvention can be used in the context of other environments, includingother electrical pluggable modules.

[0040] Reference is initially made to FIGS. 1A-1D and FIGS. 2A-2E, whichtogether illustrate one presently preferred embodiment of a transceivermodule, designated generally at 100. As shown in FIGS. 1A and 1C, thetransceiver module 100 includes a top housing portion 105, a printedcircuit board (“PCB”) 110, and a bottom housing portion 115. The top andbottom housing portions 105, 115 are designed to fit together and forman interior portion containing a PCB 110 and associated electronic andoptical components. A set of screws 116 (or any other appropriatefastening mechanism) are used to fasten the two housing portions 105,115 together to form the outer shell, or outer housing 103, of thetransceiver module 100. When joined together, the top and bottom housingportions 105, 115 also form a front opening 117 and a rear opening 118.The front opening 117 is designed to accept a modular plug (not shown)that is connected to two optical waveguides, one input waveguide and oneoutput waveguide (not shown), the structure and implementation of whichare well known in the art of optical communications. The rear opening118 is designed to expose an electrical edge connector, denoted at 112,formed along one end of the PCB 110. The edge connector 112 is capableof being electrically and physically received within a correspondingconnector (such as is shown in FIG. 8A at 702) that is typically mountedon a host board (700 in FIG. 8A) of an appropriate host device (notshown). The housing portions 105, 115 can include multiple holes or gapsthat allow heat to escape from inside the transceiver module 100 duringoperation.

[0041] In a preferred embodiment, the top and bottom housing portions105, 115 are at least partially composed of a conductive material sothat when the housing portions are joined together, a shell ofconductive material is formed about the periphery of the transceivermodule 100. The conductive material on the housing portions 105, 115form what is known as the chassis ground. A ground is an electricalpathway or drop through which voltage can pass. As discussed below, aground can also have electromagnetic effects. The chassis ground iselectrically isolated from all circuitry on the PCB 110.

[0042] As noted, the PCB 110 is substantially positioned within theinterior portion formed between the top and bottom housing portions 105,115. The top and bottom housing portions 105, 115 contain varioussupport structures to securely support the PCB 110 when the two housingportions are joined together. FIGS. 2A-2C illustrate a completedtransceiver module 100 in which the PCB 110 is securely positionedbetween the top and bottom housing portions 105, 115. The PCB 110includes a top surface 110A oriented toward the top housing portion 105,and a bottom surface 110B oriented toward the bottom housing portion115.

[0043] The PCB 100 further includes a plurality of high speed traces 140that electrically transfer data from one location to another.Specifically, the PCB 100 includes edge traces 140A that are located onboth the top and bottom surfaces 110A and 110B of the edge connector112, and connecting traces 140B located on the surface of the top PCBsurface. Because data are being transmitted at a very high frequency inan electrical form, potentially harmful EMI waves are generated withinthe transceiver module 100. The type of EMI waves that are allowed toleak out of the transceiver module 100 is dependent on the size andposition of any opening present in the housing. Moreover, if the housingportions 105, 115 were not grounded, EMI would not be efficientlycontained.

[0044] The largest opening present in the housing of a typical prior arttransceiver module is located at the rear end of the housing, designatedat 119, where the edge connector of the PCB 110 is exposed so as toelectrically connect with a corresponding connector. As noted, the rearopening 118 located at the rear housing end 119 must provide a minimumclearance for the PCB 110 so as to not interfere with the electricalsignals present on the high speed traces 140A and 140B communicatingwith the edge connector 112. In known devices, the largest openingdistance is generally measured diagonally across an opening (denoted asthe dimension “X” in FIG. 7C) because this is the longest onedimensional length of space available. The length of the largest openingis mathematically related to the frequencies of EMI waves that areallowed to leak out of the transceiver module. As data are transferredfaster, the operating frequencies of the electrical components increase;thus the frequency of emitted EMI increases. Because frequency isinversely proportional to wavelength, the higher the frequency, theshorter the relative wavelength of the EMI waves that are generated bythe high speed data. Therefore, in order to reduce the leakage of EMIwaves generated from higher frequency data transmissions, the largestopening distance must be decreased. Unfortunately, the opening at therear of the transceiver module cannot be entirely eliminated because ofthe high speed traces that are located on the surface of the PCB. Asmentioned, there must be some space between the housing portions, whichare grounded at chassis ground, and the conductive traces that passthrough rear opening of the transceiver module in order to avoid signaldegradation of the signals passing through the traces.

[0045] Continuing reference is made to FIGS. 1A-2E. Embodiments of thepresent invention provide a means for reducing the size of the opening,thereby minimizing the amount of EMI that can escape therethrough. Forexample, in the illustrated embodiment, the PCB 110 includes at leasttwo holes that extend through the entire thickness of the boarddesignated at 110. The holes are lined with a conductive material toform electrically conductive vias 120. FIG. 2E illustrates how the holesare lined to create the vias 120. The vias 120 are formed in the board110 in a manner as to be electrically isolated from the remainder of thecircuitry on the PCB 110. As will be seen, the conductive vias 120enable a “chassis ground fence” to be created adjacent the rear housingend 119 in order to reduce the emission of EMI from the interior of thetransceiver module 100.

[0046] In the illustrated embodiment, the top housing portion 105includes a raised structure 104 located at the rear housing end 119adjacent the rear opening 118. As best seen in FIG. 1D, the raisedstructure 104 includes two posts 125 oriented toward the bottom housingportion 115. The posts 125 are positioned to be received within theholes defining the conductive vias 120 when the top and bottom housingportions 105, 115 are joined together. Thus, the posts 125 serve toalign the PCB 110 with respect to the top housing 105. With the posts125 aligned with and partially received into the conductive vias 120,two plates 122 formed on the raised structure 104 of the top housingportion 105 are brought into contact with conductive portions on theouter periphery of the conductive vias 120. The plates 122 are formed ofan electrically conductive material that enables them to electricallyconnect with the conductive vias 120 and to contribute in establishingchassis ground when the top and bottom housings 105, 115 are joinedtogether, as will be seen. This arrangement is best seen in FIG. 2E,which shows the plates 122 in electrical contact with the conductiveplating of vias 120, thereby establishing electrical contact betweenvias 120 and top housing 105.

[0047] As best seen in FIGS. 1B and 2E (in cross section), the bottomhousing 115 includes two plates 130 that are positioned on a ridge 132of the bottom housing as to be aligned with the conductive vias. In thisalignment, the plates 130 are positioned such that they physicallycontact the exterior periphery of the conductive vias 120 when the topand bottom housing portions 105 and 115 are joined. The plates 130 arealso composed of a conductive material and are electrically connected tothe bottom housing 115. This enables the plates 130 to participate inconducting chassis ground between the top and bottom housing portions105 and 115 when the housing portions are joined, as shown in FIG. 2A.The plates 122 of the top housing portion 105 and the plates 130 of thebottom housing portion 115 are positioned such they only electricallyconnect with the vias 120 and are electrically isolated from all othercircuitry on the PCB 110.

[0048] In greater detail, because the plates 122 of the top housing 105are electrically connected to the conductive vias 120 defined in the PCB110, and the vias are electrically connected to the plates 130, the tophousing 105 is in indirectly and electrically connected to the bottomhousing 115 by way of a conductive pathway that extends through theconductive vias and each set of plates when the housing portions areclamped into contact with one another. Thus, a chassis ground present atone or both of the housing portions 105, 115 is extended through theconductive pathway, as just described. The extension of chassis groundthrough this conductive pathway creates what is referred to herein as a“chassis ground fence.” As explained below, this chassis ground fencereduces the escape of EMI from the transceiver module, thereby improvingthe performance of the transceiver.

[0049]FIG. 2E illustrates a close-up cross sectional view of a portionof the chassis ground fence. Accordingly, this figure shows one post125, one plate 122, one complete conductive via 120, and one plate 130as arranged when the top and bottom housing portions 105 and 115 arejoined to form the transceiver module housing. The physical connectionbetween these components is evident in the figure, thereby giving riseto the electrical connection between the top housing portion 105 and thebottom housing portion 115.

[0050] As can be seen from FIGS. 2A-2E, the rear opening 118 of the rearhousing end 119 is divided and reduced in dimension as a result of thepresence of the chassis ground fence defined by the posts 125, plates122, conductive vias 120, and plates 130. Specifically, these structuresintroduce portions of the chassis ground through formerly open areadefined by the rear opening 118 (see, in comparison, dimension “X” inFIG. 6B) to define two reduced dimension openings 136 and 138. Becauseof the chassis ground fence and the corresponding reduction in theoverall dimension of the rear opening 118, EMI is unable to effectivelypenetrate the rear housing end 119 through the reduced dimensionopenings 136. This in turn reduces EMI emission from the transceivermodule 100 and prevents interference with operation of either thetransceiver or other nearby components. The reduced dimension openings136 and 138 remain sufficiently sized to allow the connecting traces140B to pass through without affecting the quality of the signals theycarry.

[0051] It will be appreciated that the specific configuration of thechassis ground fence defined by the above components can be varied whilestill providing the desired EMI protection. For instance, the number ofplate-via-post-plate combinations can be varied to increase or decreaseboth the number and size of the reduced-dimension openings at the rearhousing end 119. Additionally, the presence, particular shape, andconfiguration of the raised structure 104 of the top housing 105, aswell the ridge 132 supporting the plates 103 of the bottom housing 115can also be modified as desired to achieve optimum function. In oneembodiment, for instance, the height of the raised structure 104 can bealtered in order to vary the clearance provided between the top housing105 and the surface of the PCB 110 on which the connecting traces 140Bare located. These and other changes to the chassis ground fence arecomplicated.

[0052] As seen in FIG. 2E, though they align with and may be inelectrical contact with the conductive vias 120, the posts 125 in theillustrated embodiment do not completely extend through the vias todirectly contact any portion of bottom housing 115. Indeed, directcontact between the posts 125 and the bottom housing 115 is notnecessary to extend chassis ground between the top and bottom housingportions 105 and 115. Rather, chassis ground in the illustratedembodiment extends along multiple paths comprising one each of theplates 122, conductive vias 120 and plates 130. If desired, however,each post 125 can be configured in one embodiment to electricallyconnect with the respective conductive via 120 into which it isreceived, thereby contributing to the provision of chassis groundbetween the top and bottom housings 105, 115.

[0053] In view of the above discussion, it is seen that the combinationof the plates 122, the conductive vias 120, the posts 125, and theplates 130 serve as one means for electrically connecting the top andbottom housing portions 105 and 115 while reducing the area of EMIemission at an end of the transceiver module 100 proximate the edgeconnector 112. However, it is appreciated that other means can be alsoemployed to achieve this same functionality. For example, alternativestructures, such as conductive foams and springs, could be utilized inestablishing an electrical chassis ground connection between the tophousing 105 and the bottom housing 115. These alternative embodiments,in addition to other embodiments to be explicitly described below, aretherefore contemplated within the claims of the present invention.

[0054] Reference is next made to FIGS. 3A-3D and FIGS. 4A-4E, whichillustrate a transceiver module, designated generally at 200, configuredin accordance with another embodiment of the present invention. Thetransceiver module 200 includes many of the same components as theembodiment described in detail with reference to FIGS. 1A-1D and FIGS.2A-2E, and to the extent that common features are shared between them,some of these features will not be discussed. As shown in the figures,the module 200 includes a top housing portion 205, a bottom housingportion 215, and a PCB 210. As described above, the top and bottomhousing portions 205, 215 fit together to form an outer housing 203 thatat least partially encloses the PCB 210. In addition, this outer housing203 carries an electrical chassis ground around the PCB 210 in the samemanner as described above. Extending from a rear housing end 219 of themodule 200 is an edge connector 212 portion of the PCB 210. The edgeconnector 212 includes a plurality of conductive edge traces 240A incommunication with connecting traces 240B for transferring electricaldata signals between the module 200 and a host device (not shown) thatinterfaces with the edge connector.

[0055] In the illustrated embodiment, the PCB 210 further includes twoholes 220 formed through the PCB. Unlike the embodiment described above,the holes 220 are not lined with any conductive material but are simplyformed through the dielectric material comprising the PCB 210. The holes220 are located substantially adjacent the edge connector 212 portion ofthe PCB 210.

[0056] The top housing portion 205 includes two bosses 225, best seen inFIGS. 3C and 3D, that are positioned on a raised structure 204 of thetop housing 205 so as to be received within the corresponding holes 220when the top and bottom housing portions 205 and 215 are joinedtogether. Specifically, FIGS. 3D and 4E illustrate how the sockets 225are received within the holes 220. Each socket 225 is composed of anelectrically conductive material and is electrically connected to thetop housing 205. In this way, the sockets 225 are connected to chassisground when the top housing portion 205 is chassis grounded.

[0057] The bottom housing portion 215 includes two pins 230 positionedon a ridge 232 that are to be partially received within the holes 220defined in the PCB 210. In particular, the pins 230 are configured as tobe received within corresponding sockets formed in the ends of thebosses 225 when the top and bottom housing portions 205, 215 are joinedtogether. This is best shown in FIG. 4E. Like the bosses 225, the pins230 are also composed of an electrically conductive material and areelectrically connected to the bottom housing portion 215 so that thepins are connected to chassis ground when the bottom housing portion 215is chassis grounded.

[0058] The alignment described above enables the holes 220, bosses 225,and pins 230 to form electrically conductive paths between the top andbottom housings 205 and 215 when the housing portions are joinedtogether. In particular, when the housing portions 205 and 215 arejoined, each pin 230 partially passes through the corresponding hole 220and is received into the socket formed in the corresponding boss 225(the boss also being partially received by the hole) such that the pinand boss are electrically connected. Because it is not plated with aconductive material, the hole 220 does not contribute to the electricalconnection between the pin 230 and the boss 225 in contrast to theprevious embodiment, but rather merely provides space for them toconnect. As such, the PCB 210 and any circuitry located thereon areelectrically isolated from any of the bosses 225 or pins 230.

[0059] As was the case with the previous embodiment, when the top andbottom housing portions 205, 215 are joined together, the electricallyconductive paths established therebetween via the boss-hole-pinconfiguration form multiple chassis ground paths between the housingportions when one or both housing portions are chassis grounded. Asbefore, the chassis ground passes through the PCB 210 between the topand bottom housings 205 and 215 via the boss-hole-pin configuration toform a chassis ground fence. Again, as with the previous embodiment, thechassis ground fence reduces the overall size of the opening (i.e., rearopening 218) at the rear housing end 219 by sub-dividing it intosmaller-dimensioned openings, designated at 236 and 238. The openings236 and 238 are sufficiently sized as to enable the connecting traces240B to pass therethrough without impairing the signals they carry. FIG.4E illustrates the maximum dimension of one of the openings, opening238, as comprising a distance 235. As can be seen in comparison with theopening 20 of the prior art transceiver shown in FIG. 6B, the dimension235 of the opening 238 is substantially smaller than dimension X of theopening 20. As before, this relatively reduced dimension of the openings236 and 238 at the rear housing end 219 results in reduced EMI emissionsescaping from the rear housing end of the transceiver module 200. Again,absent the two sets of holes 220, sockets 225, and pins 230, the openingdistance would span an area much greater than that defined by the tworeduced dimension openings 236, 238, thereby undesirably increasing thearea of escape for EMI. As before, it should be remembered that theparticular hole-boss-pin configuration shown in the present embodimentis merely exemplary of the structure that can be utilized in providing achassis ground fence for containing EMI in a transceiver module. Otherconfigurations that preserve this function are also contemplated.Additionally, it is appreciated that the chassis ground fence conceptcan be extended to areas of the transceiver module other than the rearhousing end, if desired.

[0060] Reference is now made to FIGS. 5A-5B, which illustrate yetanother embodiment of the present invention. Again, to the extent thatcommon features are shared between this and previous embodiments, someof these features will not be discussed. FIGS. 5A and 5B include viewsof a portion of an optical transceiver module 300 having top and bottomhousing portions 305 and 315, respectively. The top and bottom housingportions 305 and 315 together form the transceiver housing, whichcontains a PCB 310. Similar to the previous embodiment, the PCB 310includes two holes 320 defined therethrough near an end thereof, the endbeing located substantially adjacent a rear housing end 319 of thetransceiver module 300. The holes 320 are not lined with a conductivematerial and are aligned to each receive a post 325 extending from andelectrically connected to a portion of the top housing portion 305. Eachpost 325 extends through the respective hole 320 and contacts a portionof the bottom housing portion 315, in this case, one of two plates 330,which are electrically connected with the bottom housing portion.

[0061] The engagement of each post 325 with the respective plate 330creates a conductive path that electrically connects the top housingportion 305 to the bottom housing portion 315. Further, this connectionenables chassis ground to be extended through the conductive path,thereby forming a chassis ground fence at the rear housing end 319 ofthe transceiver module 300, as in previous embodiments. In contrast toprevious embodiments, however, each post 325 completely extends throughthe respective hole 320 of the PCB 310 to contact the respective plate330 of the bottom housing portion 315. In other embodiments, the post325 can extend through the hole 325 and directly contact a flat surfaceof the bottom housing portion 315, thereby obviating the need for theplate 330. Or, in yet another embodiment, the post-hole-plateconfiguration can be modified by plating each hole 320 with a conductiveplating similar to that found in the embodiment illustrated in FIGS.1A-2E, further enhancing the electrical contact between the housingportions. The present embodiment, in addition to the previous andfollowing embodiments, therefore serves as another example of a meansfor electrically connecting the top and bottom housing portions withchassis ground as to reduce the area of emission of electromagneticinterference from an end of the transceiver module.

[0062] Reference is next made to FIGS. 6A-6B, which illustrate a printedcircuit board, designated generally at 500, configured in accordancewith yet another embodiment of the present invention. The printedcircuit board 500 in this embodiment is designed to fit within thehousing of a transceiver module. However, the EMI reductionmodifications are implemented on the printed circuit board 500 alone.Therefore, the printed circuit board 500 described in this embodimentcan be utilized with existing unmodified housings of the same formfactor to form a complete transceiver module. The printed circuit board500 includes high speed edge traces 520 positioned on the edge connectorportion 512 of the printed circuit board 500. The high speed edge traces520 are electrically connected to embedded traces 525 that tunnelthrough the dielectric material within the printed circuit board and arethen electrically connected to median traces 530. The median traces 530are positioned on the surface of the printed circuit board 500 like thehigh speed edge traces 520 as illustrated in FIG. 6A. The printedcircuit board 500 further includes two electrical vias 535. Theelectrical vias 535 are narrow holes that extend through the entireprinted circuit board 500 that are filled with an electricallyconductive material. The vias 535 are electrically isolated from allother circuitry on or within the printed circuit board 500. These vias535 provide a connection point to the module housing such that a chassisground can extend through the printed circuit board. Only one side ofthe vias 535 need be electrically connected to the housing in order toencircle the embedded traces 525 with the chassis ground because of anembedded ground layer 540, described below.

[0063] The cut-away view illustrated in FIG. 6B shows how the printedcircuit board further includes an embedded ground layer 540 thatencircles the embedded traces 525. The embedded ground layer 540 iselectrically connected to the vias 535 in order to carry the chassisground from the housing. The embedded ground layer 540 is a conductivematerial that is embedded within the printed circuit board in the mannershown in FIG. 6B. By incorporating this embedded ground layer 540 thatcarries the chassis ground, particular EMI waves generated within thehousing are effectively prevented from leaking out. The printed circuitboard 500 in this embodiment is designed to fit within a housing thatcompletely eliminates a rear opening by actually touching the printedcircuit board 500 at a lateral location between the high speed edgetraces 520 and the vias 535. Since all electrical data within thisregion is transferred through the embedded traces 525, it is possiblefor the housing to physically contact the printed circuit board(completely eliminating the open space that commonly allows EMI waves toleak out) without electrically interfering with the transference ofdata. As described above, the vias 535 can be equipped with conductivedevices known in the art to ensure that an electrical connection betweenthe vias 535 and the housing (not shown) is established, such as aconductive foam or spring. In addition, the embedded ground of thisembodiment can be combined with the interconnection schemes of theprevious embodiments to provide a different electrical connectionbetween the printed circuit board 500 and the housing (not shown).

[0064] In one embodiment, in order to further facilitate reliableelectrical connection between the top housing and the vias 535 andbetween the bottom housing and the vias 535, a conductive band 550 canbe formed around the surface of the PCB 500, as illustrated in FIGS. 6Aand 6B. The thickness of the conductive band 550 is exaggerated in FIG.6B for purposes of visibility in the illustration. The conductive band550 both establishes a conductive ground path around the PCB and alsoenhances the electrical connection with the top and bottom housings.This conductive band or strip 550 is particularly useful in establishinga reliable electrical connection with springs or foam EMI gaskets thatcan be used with the top and bottom housing.

[0065] In summary, the present invention relates to a module design thatreduces the leakage of particular EMI waves by passing a ground throughor piercing a PCB that is within a grounded housing. The piercing grounddoes not affect any of the circuitry on the PCB but has the effect ofminimizing the size of any openings through which EMI can escape. Theteachings of the present invention are applicable to any electricalmodule that potentially generates high frequency data that causespotentially harmful EMI waves.

[0066] The present invention may be embodied in other specific formswithout departing from its spirit or essential characteristics. Thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. A printed circuit board (“PCB”), comprising: apiece of dielectric material including circuitry and an edge connectorportion; an edge trace located on a surface of the edge connectorportion; an embedded trace substantially disposed within the dielectricmaterial, the embedded trace electrically connecting the edge trace witha corresponding median trace located on a surface of the dielectricmaterial, the median trace being in communication with at least some ofthe circuitry; an embedded ground structure disposed within thedielectric material and at least partially encircling the embeddedtrace; and a conductive element passing substantially through thedielectric material and being electrically connected to the embeddedground structure.
 2. The PCB as recited in claim 1, wherein thecircuitry is configured for use in connection with the operation of oneor more optoelectronic components.
 3. The PCB as recited in claim 1,wherein the PCB substantially conforms with applicable requirements ofone of: the SFP MSA; and, the XFP MSA.
 4. The PCB as recited in claim 1,wherein the embedded ground structure is positioned for electricalcommunication with a module housing when the PCB is disposed therein. 5.The PCB as recited in claim 1, wherein the conductive element passessubstantially vertically through the dielectric material.
 6. The PCB asrecited in claim 1, wherein the conductive element is positioned betweenthe edge trace and the median trace.
 7. The PCB as recited in claim 1,wherein the embedded ground structure comprises a pair of ground planesdisposed above and below, respectively, the embedded trace.
 8. The PCBas recited in claim 1, wherein the conductive element comprises aconductive via.
 9. The PCB as recited in claim 1, wherein the conductiveelement is substantially electrically isolated from the circuitry. 10.The PCB as recited in claim 1, wherein the conductive element ispositioned for electrical communication with a module housing when thePCB is disposed therein.
 11. The PCB as recited in claim 1, wherein theconductive element is configured to electrically communicate with amodule housing by way of one of: an EMI gasket; and, a spring.
 12. ThePCB as recited in claim 1, further comprising a conductive bandextending around at least a portion of the dielectric material and beingin electrical communication with the conductive element.
 13. The PCB asrecited in claim 12, wherein the conductive band is positioned so as toat least partially encircle the embedded trace.
 14. A printed circuitboard (“PCB”) for use in an electronic module that includes a housing,the PCB being substantially disposed within the housing and comprising:a piece of dielectric material including circuitry and an edge connectorportion; an edge trace located on a surface of the edge connectorportion; an embedded trace substantially disposed within the dielectricmaterial, the embedded trace electrically connecting the edge trace witha corresponding median trace located on a surface of the dielectricmaterial, the median trace being in communication with at least some ofthe circuitry; an embedded ground structure disposed within thedielectric material and at least partially encircling the embeddedtrace; and a conductive element passing substantially through thedielectric material and being electrically connected to the embeddedground structure and to the housing of the electronic module.
 15. ThePCB as recited in claim 14, wherein the circuitry comprises circuitryfor use in connection with one or more optoelectronic components. 16.The PCB as recited in claim 14, wherein the PCB substantially conformswith applicable requirements of one of: the SFP MSA; and, the XFP MSA.17. The PCB as recited in claim 14, wherein the embedded groundstructure is in electrical communication with the module housing. 18.The PCB as recited in claim 14, wherein the conductive element passessubstantially vertically through the dielectric material.
 19. The PCB asrecited in claim 14, wherein the conductive element is positionedbetween the edge trace and the median trace.
 20. The PCB as recited inclaim 14, wherein the embedded ground structure comprises a pair ofground planes disposed above and below, respectively, the embeddedtrace.
 21. The PCB as recited in claim 14, wherein the conductiveelement comprises a conductive via.
 22. The PCB as recited in claim 14,wherein the conductive element is substantially electrically isolatedfrom the circuitry.
 23. The PCB as recited in claim 14, wherein theconductive element is in electrical communication with the modulehousing.
 24. The PCB as recited in claim 14, wherein the conductiveelement is configured to electrically communicate with the modulehousing by way of one of: an EMI gasket; and, a spring.
 25. The PCB asrecited in claim 14, further comprising a conductive band extendingaround at least a portion of the PCB and being in electricalcommunication with the conductive element.
 26. The PCB as recited inclaim 25, wherein the conductive band is positioned so as to at leastpartially encircle the embedded trace.
 27. A printed circuit board(“PCB”) for use in an optical transceiver module that includes anoptical transmitter and an optical receiver substantially disposedwithin a housing, the PCB being substantially disposed within thehousing of the optical transceiver module and comprising: a piece ofdielectric material including circuitry and an edge connector portion,at least some of the circuitry being in communication with at least oneof: the optical transmitter; and, the optical receiver; a plurality ofedge traces located on a surface of the edge connector portion andconfigured to electrically interface with a host system; a plurality ofembedded traces substantially disposed within the dielectric material,each embedded trace electrically connecting an edge trace with acorresponding median trace located on a surface of the dielectricmaterial, the median traces being in communication with the circuitry;an embedded ground structure disposed within the dielectric material andsubstantially encircling the plurality of embedded traces; and at leasttwo conductive vias passing through the dielectric material and beingtelectrically connected to the embedded ground structure and to thehousing of the optical transceiver module.
 28. The PCB as recited inclaim 27, wherein the PCB substantially conforms with applicablerequirements of one of: the SFP MSA; and, the XFP MSA.
 29. The PCB asrecited in claim 27, wherein the at least two conductive vias arepositioned between the plurality of edge traces and the median trace.30. The PCB as recited in claim 27, wherein the at least two conductivevias are configured to electrically communicate with the module housingby way of one of: an EMI gasket; and, a spring.
 31. The PCB as recitedin claim 27, further comprising a conductive band extending about atleast a portion of the PCB and being in electrical communication withthe at least two conductive vias.
 32. The PCB as recited in claim 31,wherein the conductive band is positioned so as to substantiallyencircle the plurality of embedded traces.